The present invention relates to a rotary piston valve arrangement, for a pneumatic settling tank, and includes rotary piston valves disposed in a common housing, with a first rotary piston valve being designed for the control of an additive stroke, and a second rotary piston valve being designed for the control of a discharge operation.
A rotary piston valve arrangement of the aforementioned general type is disclosed in German Patent No. 34 00 659 and refers extensively to German Patent No. 26 54 593 for its particular manner of operation. German Patent No. 34 00 659 discloses a particular embodiment of a rotary piston valve arrangement where the double rotary piston valve that is disposed in the bottom half of the housing serves merely for the control of the discharge for the air that is supplied from the upper rotary piston valve as additive strokes of the settling chamber of the pneumatic settling tank, so that the double rotary piston valve merely has discharge windows, and the bottom half of the housing is provided with associated air outlet openings.
Proceeding from the embodiment described in German Patent No. 34 00 659 where the speed of the rotary piston for the additive control of the air inlet is four times the speed of the double rotary piston valve for the control of the discharge, the known rotary piston valve arrangement has the drawback that at the same time as the fourth air introduction of the inlet rotary piston valve, the lower double rotary piston valve reaches its discharge position, so that the air that was to be supplied to the settling chamber with the fourth air introduction flows directly away, without effect, to the air outlet openings via the rotary pistons of the double rotary piston valve, so that a portion of the energy expended for generating the flow of air is not converted.
It is therefore an object of the present invention to improve a rotary piston valve arrangement of the aforementioned general type in such a way that during operation of a settling tank that is controlled with a double rotary piston valve arrangement, the air throughput is reduced.